ARM: dts: msm: configure supply property for DSI on msm8998.

This change adds the property to turn off supplies
(gdsc and vdda-0p9) while transitioning to
low power/idle power collapse. vdda-0p9 can be turned
off only while transitioning to low power state, while gdsc
can be turned off in both idle power collapse and low power
state transition.

CRs-Fixed: 2009863
Change-Id: I4e382b763a04839d7371a57e53aea4cfca19cb1f
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>